A wide variety of seat belt retractors for vehicles have been developed for occupant safety. These seat belt retractors commonly comprise a reel which is biased by a spring in order to retract the seat belt against the occupant during use and to rewind the seat belt on the reel upon termination of use by the occupant. In order to retract and rewind the belt effectively, it is common for these springs to apply a relatively considerable retraction force to the reel. In some instances, however, this retraction force tends to be uncomfortable to the occupant. As a result, it desirable to provide seat belt retractors with a tension-relieving mechanism for reducing this retraction force upon the occupant.
In this connection, a number of tension-relieving mechanisms have been developed for seat belt retractors. For instance, one such tension-relieving mechanism operates automatically upon certain predetermined seat belt manipulations. In particular, it is actuated into its tensionless, comfort mode upon the user first extending the seat belt about the torso and shoulder region to secure its tongue in a latch device. Upon the act of latching the seat belt, a slight retraction of the belt occurs. This subsequent slight retraction causes an internal locking pawl to engage a ratchet wheel fixed to the reel shaft to prevent continued rewinding of the belt onto the reel under the force of the retraction spring. Thus, the occupant's shoulder region is relieved of the retraction spring force provided to rewind the seat belt. Examples of such devices are disclosed in U.S. Pat. Nos. 3,851,836, 3,869,098 and 3,834,646.
Also, some tension-relieving mechanisms include a memory system. A memory system allows the occupant to move slightly forward to protract one or two inches of the belt from the retractor without canceling the tension-relieving mechanism. For instance, if the occupant returns to his initial position following a slight forward movement, the tension-relieving mechanism remains operative to continue relieving the retraction force.
However, if the occupant maneuvers so to protract the belt more than a predetermined amount, a memory distance amount, the tension-relieving mechanism is automatically actuated to its ineffective or release position. Then, the retraction spring is allowed to retract the belt tightly against the occupant under a full retraction force.
In addition, certain mechanisms include a door operated release mechanism to assure that the seat belt is fully wound upon an occupant's departure from the vehicle. More specifically, the door operated release mechanism senses an opening of the door and, in response, actuates the tension-relieving mechanism to its inoperative position, thereby enabling the retraction spring to rewind the belt under full retraction force to its complete wound position.
Another known tension-relieving mechanisms is directed toward activation upon some conscious effort of the occupant. For instance, one device includes an occupant actuation switch to actuate the tension-relieving mechanism. In particular, the switch closes a circuit which energizes a solenoid for shifting the locking pawl into engagement with the ratchet wheel. This operation places the tension-relieving system into its tension-relieving state regardless of the amount of belt protraction. As a result, belt slack in the seat belt is not removed when the switch is actuated, even if the occupant leans backward against the seat after such actuation.
One such tension-relieving system is disclosed in U.S. Pat. No. 4,585,185, wherein this system is rendered inoperative upon a subsequent operation of the switch means. Thus, manipulation of the belt beyond a memory distance will not render automatically the tension-relieving mechanism ineffective for allowing the retraction spring to rewind the belt. This is because the solenoid has shifted the tension-relieving pawl into position, and an electrical switch operation is required to shift the solenoid for moving the pawl to its release position. U.S. Pat. No. 4,919,450 discloses the broad concept of using a manual overt actuator to shift a tension-relieving means to an activated state, and to remove belt slack such that a subsequent slight belt protraction will shift the tension-relieving means to a tensionless state. The illustrated overt actuator is a switch and solenoid or a lever and cable to shift the tension-relieving to its activated state after the occupant pushes the switch or lever.